Calcium channels play a fundamental role a in variety of neuronal processes including neurotransmitter release, neurite extension and electrical signalling. Calcium ions flowing through voltage- dependent calcium channels, operate as an intracellular second messenger by modulating various cellular constituents. In the hippocampus, calcium ions are also involved in the form of memory called long-term potentiation and may be involved in diseases such as epilepsy. The existence of multiple types of neuronal calcium channels is now widely accepted. Our work demonstrated that chick DRG neurons had three different types of calcium channels which we call "T", "N", and "L". These channels differed on the basis of pharmacology, single-channel conductance, and gating. The studies outlined in this grant would extend the Ca channel investigations into several different areas of the hippocampus, including the CA1, CA3 and dentate-gyrus regions. Patch-clamp electrophysiology and high-K+ or field electrode evoked release of radiolabelled neurotransmitters, will be the principal techniques used. Specifically, I propose to carry out the following studies. -1) Characterize the calcium present in hippocampal neurons. Both Ca channel getting and permeation will be investigated. -2) Study hippocampal calcium channel modulation by neurotransmitters, hormones and drugs. These experiments will focus mainly on single-channel mechanisms. Perfusion of the patch pipette while in the whole-cell recording configuration will allow us to introduce and study various intracellular second- messengers. -3) Try to correlate calcium types with cellular function. Included will be studies attempting to identify the type(s) of Ca channels involved in neurotransmitter release. -4) Prepare giant synaptosomes to directly investigate pre- synaptic calcium channels with electrophysiological techniques. One of the most interesting aspect of these studies will the comparisons made between the calcium channels found in the different hippocampal neurons.